As used herein, the term “concrete” means and refers to a mixture of a hydratable cementitious binder (e.g., Portland cement), fine aggregate (sand), and coarse aggregate (crushed stone or gravel) to which water is added to provide a composition that can harden into a building structure (e.g., foundation) or a civil engineering structure (e.g., tunnel) or other structural component.
In World Patent Application No. PCT/US98/12876, which is incorporated by reference herein, Jardine et al. disclosed that oxyalkylene-containing polymer additives, used as plasticizing or water-reducing admixtures in concrete, sometimes had unpredictable dosage behavior in different concrete mixes. Jardine et al. found that the aggregates contained in some concrete mixes had certain swellable clays (e.g., smectites) that negatively interacted with the plasticizer to create poor dosage response. It was theorized that such clays expanded when initially wetted by the mix water, and, in the expanded state, absorbed or entrapped the plasticizer. The invention of Jardine et al. was to employ clay-modifying agents. The purpose was to modify the clay activity, or mechanism, by which the clay-bearing aggregate interfered with the plasticizer activity, thereby to permit normal dosage of plasticizer to be used in the concrete.
The present inventors have discovered that, where an oxyalkylene-containing polyol polymer is used as the clay-modifying agent, the resultant concrete mix may have air entrainment problems, even when conventional air entraining agents (“AEAs”) are used. One of the objectives of the present invention, therefore, is to improve the air entrainment capability and air void quality of concrete mixes that employ oxyalkylene plasticizers and clay activity modifying agents. Another objective, more generally, is to provide a surface active agent system that is believed to be useful for adjusting and stabilizing air void systems in cementitious compositions, without seriously impeding the ability to employ conventional AEAs and/or clay-activity-modifying agents.
Technically speaking, an AEA does not generate air in the concrete, but merely stabilizes air that is (1) infolded (or mechanically enveloped) during mixing; (2) dissolved in the mix water; and/or (3) present in the intergranular spaces in the dry cement and aggregate. The concept of “entrained” air voids is different from the concept of “entrapped” air voids. It is desirable (e.g., for purposes of increasing durability of hardened concrete under freeze-thaw conditions) to entrain air voids of a certain size (average diameter typically between 0.01-1.0 millimeter) and shape (generally spherical) in the paste portion of the wet concrete. Examples of common or conventional AEAs include water soluble salts (usually sodium) of wood resins, wood rosins, lignosulfonic acid, sulfonated hydrocarbons, proteinaceous materials, and fatty acids (e.g., tall oil fatty acid) and their esters.
The problem of controlling air void content and size distribution in concrete using AEAs is especially challenging when clay modifying agents, having a tendency to detrain intentionally entrained air, are present. When AEAs are added to concrete, they form a film at the interface between the air void and water phases, due to their varying solubility in the aqueous phase. (see e.g., “Air Entraining Admixtures,” from Concrete Admixtures, Dr. Vance Dodson (Van Nostrand Reinhold, New York 1990), page 133-134). Furthermore, AEAs may be anionic, cationic, or nonionic in nature. Since common AEAs vary widely in composition and nature, a variation in their effectiveness might be expected. However, achieving consistency in managing the air content has been, for the most part, highly unpredictable.